The long term objectives of this project are to examine the mechanics and physiology of elastic mechanisms in the refilling of hearts. The elastic system in human hearts consists of the collagenous connective tissues that surround the muscles, or the connective tissues contained within the muscles themselves. The elastic system functions to assist in refilling the heart during diastole by releasing the strain energy that is stored in the connective tissue as the wall of the heart thickens during systole. This elastic mechanism may play a very important role in the cardiac cycle; evidence of this is provided by some connective tissue diseases where cardiomyopathies initiated by the disease itself create cardiac dysfunction that are out of proportion to the myocardial dysfunction. This proposal is for a small grant that will initiate research to develop a simple invertebrate heart as a model of a human heart. The lobster heart has been chosen, since it functions mechanically as the human heart, but unlike the human heart, the elastic system of the lobster heart is physically separated, and consists of suspensory ligaments that function as tensile elastic elements. The specific aims of this proposal are to characterize the nature of the elastic behaviour, and the dynamic mechanical properties of the cardiac suspensory ligaments of the lobster Homarus ainericanus. This information will then be used in future physiological studies that will partition the energy produced by the cardiac muscles of the lobster heart, and thus fully evaluate the importance of elastic refilling in this simple heart. Experimental procedures that reduce the elastic properties of the suspensory ligaments can then be used to simulate cardiac behaviour created by connective tissue diseases, and thus evaluate potential cardiac dysfunctions induced by a reduction in elastic refilling.